fixing #2021
fixing #2021

This tiny commit fixes a routing problem for proxy requests. The
router was expecting a url path behind the proxy id, if none was
given (read: the service proxied was at the root of a host) then
the router would return a 404. With this patch it now propperly
uses ProxyDataSourceRequest.

grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana